[Paper Review] Identification of the superconductivity in bilayer nickelate La$_3$Ni$_2$O$_7$ upon 100 GPa

Jing Li, Peng, Di+15 more|arXiv (Cornell University)|Apr 17, 2024

Magnetic and transport properties of perovskites and related materials5 citations

TL;DR

The study demonstrates bulk superconductivity in La3Ni2O7 under high pressure, with a Tc onset of 83 K at 18 GPa, a structural transition around 40 GPa, and Meissner evidence up to 80 GPa, including a maximum 62.7% superconducting volume fraction at 22 GPa.

ABSTRACT

Identification of superconductivity in the Ruddlesden-Popper phases of nickelates under high pressure remains challenging. Here, we report a comprehensive study of the crystal structure, resistance, and Meissner effect in single crystals of La$_3$Ni$_2$O$_7$ with hydrostatic pressures up to 104 GPa. X-ray diffraction measurements reveal a structural transition from the orthorhombic to a tetragonal phase above 40 GPa. Zero resistance of the superconductivity was achieved with a maximum onset $T_c^{onset}$ of 83 K at 18.0 GPa. Superconductivity is gradually suppressed until it disappears above 80 GPa, resulting in a right-triangle-like superconducting region. The direct-current magnetic susceptibility technique successfully detected the Meissner effect in La$_3$Ni$_2$O$_7$ under pressure; the maximum superconducting volume fraction is estimated to be 62.7% at 22.0 GPa. Thus, we demonstrate the bulk nature of superconductivity in the bilayer nickelate La$_3$Ni$_2$O$_7$ single crystals under high pressure. The results reveal intimate connections among the superconductivity, oxygen content, and structure in La$_3$Ni$_2$O$_7$.

Motivation & Objective

• Motivate the search for superconductivity in Ruddlesden-Popper nickelates under extreme pressure.
• Characterize how crystal structure, electrical resistance, and magnetic response evolve under hydrostatic pressure up to ~104 GPa.
• Establish the bulk nature of superconductivity and its relationship to oxygen content and structural changes in La$_3$Ni$_2$O$_7$.
• Quantify the superconducting phase extent and volume fraction under pressure.

Proposed method

• Perform X-ray diffraction to track structural phases under pressure up to 104 GPa.
• Measure electrical resistance to identify zero-resistance onset of superconductivity.
• Use direct-current magnetic susceptibility to detect the Meissner effect and estimate superconducting volume fraction.
• Study single crystals of La$_3$Ni$_2$O$_7$ under hydrostatic pressure to correlate structure, transport, and magnetism.
• Determine the pressure dependence of Tc onset and the pressure range where superconductivity persists.

Experimental results

Research questions

• RQ1 Does La$_3$Ni$_2$O$_7$ exhibit superconductivity under high pressure up to ~100 GPa?
• RQ2 What is the Tc onset as a function of pressure, and how does it evolve with structural changes?
• RQ3 Is the observed superconductivity a bulk property, as evidenced by the Meissner effect and volume fraction measurements?
• RQ4 How are superconductivity, oxygen content, and crystal structure interrelated under pressure?
• RQ5 What is the pressure range over which superconductivity exists and how does it disappear at high pressure?

Key findings

• Zero-resistance superconductivity is observed with a Tc onset of 83 K at 18.0 GPa.
• Superconductivity gradually vanishes and disappears above 80 GPa, outlining a right-triangle-like superconducting region.
• DC magnetic susceptibility detects the Meissner effect, with a maximum superconducting volume fraction of 62.7% at 22.0 GPa.
• X-ray diffraction shows a structural transition from orthorhombic to tetragonal above 40 GPa.
• The results indicate bulk superconductivity in La$_3$Ni$_2$O$_7$ under high pressure and reveal a link between superconductivity, oxygen content, and structure.